The 1-hour glucose test is a screening for gestational diabetes, typically done between 24 and 28 weeks of pregnancy. You drink a sweet liquid containing 50 grams of sugar, wait one hour, then have your blood drawn to see how your body handled that sugar load. A result of 140 mg/dL or lower is considered normal.
How the Test Works
The test measures how efficiently your body processes a large dose of glucose. During pregnancy, hormonal changes can interfere with insulin’s ability to move sugar out of your bloodstream, which is the mechanism behind gestational diabetes. By giving you a standardized sugar load and checking your blood exactly one hour later, the test reveals whether your body is keeping up.
The sugar drink, often called glucola, is a syrupy liquid that comes in several flavors. You need to finish it within about five minutes. After that, you sit and wait for the full hour before a blood draw. The whole visit typically takes about 90 minutes when you factor in check-in time and the draw itself.
Preparation and What to Expect
The 1-hour glucose test does not require fasting. You should eat normally on the day of your appointment, and skipping meals beforehand can actually affect your results. There are a few things to keep in mind, though:
- Avoid high-sugar foods and drinks for at least one hour before the test
- Don’t chew gum or eat mints between drinking the glucola and your blood draw
- Eat a normal meal before you go, whether that’s breakfast or lunch depending on your appointment time
The glucola drink is very sweet, and some women find it unpleasant or mildly nauseating. Drinking it cold and quickly tends to make it easier to get down. Bringing something to read or do during the waiting hour helps pass the time, since you’ll need to stay at the lab or clinic.
When It’s Done
Most pregnant women take this test during the second trimester, between weeks 24 and 28. Your provider may move it earlier if you have risk factors for gestational diabetes. Some women at high risk are screened at their very first prenatal visit. Early screening is more likely if you had gestational diabetes in a previous pregnancy, have a family history of type 2 diabetes, had a BMI of 30 or higher before pregnancy, or have shown elevated glucose in your urine at routine prenatal appointments.
Understanding Your Results
A blood sugar reading of 140 mg/dL or lower at the one-hour mark is a normal, passing result. That means your body processed the sugar load effectively and no further testing is needed for gestational diabetes.
A result above 140 mg/dL does not mean you have gestational diabetes. This is an important distinction. The 1-hour test is a screening tool, not a diagnostic one. It casts a wide net on purpose, so a fair number of women who screen positive will turn out not to have the condition. What it does mean is that your provider will order a second, more involved test to find out for sure.
What Happens If You Screen Positive
The follow-up is a 3-hour glucose tolerance test, and it works differently from the screening. This time, you do need to fast for several hours beforehand. At the appointment, a blood draw is taken first to establish your fasting blood sugar level. Then you drink a larger glucose solution containing 100 grams of sugar (double the amount in the screening drink). Your blood is drawn three more times: at the one-hour, two-hour, and three-hour marks.
This test takes significantly longer and is more involved, which is why it isn’t used as the first-line screening for everyone. The 3-hour test is what actually diagnoses gestational diabetes based on how many of the four blood draws come back elevated. Many women who failed the 1-hour screening pass the 3-hour test without issue.
Why the Screening Matters
Gestational diabetes affects how your body uses sugar during pregnancy and can lead to complications for both you and the baby if it goes unmanaged. Babies born to mothers with uncontrolled gestational diabetes tend to be larger, which can complicate delivery. Blood sugar problems in the newborn right after birth are also more common. For the mother, gestational diabetes raises the risk of high blood pressure during pregnancy and increases the likelihood of developing type 2 diabetes later in life.
The good news is that gestational diabetes, when caught through screening, is very manageable. Most women control it through dietary changes and monitoring their blood sugar at home. The 1-hour glucose test exists specifically because early detection makes a real difference in outcomes, and the test itself is quick, low-risk, and requires no special preparation beyond avoiding a sugary snack beforehand.